As bandwidth requirement in a wireless communication system continues to increase, the necessity for a user equipment (UE) to utilize both a licensed frequency spectrum and an unlicensed frequency spectrum has increased. However, without coordination from a network, it could be difficult for multiple UEs to share the same unlicensed spectrum. FIG. 1A illustrates a typical wireless network 100 in which a UE 103 utilizes both a licensed spectrum and an unlicensed spectrum. The typical wireless network may include not limited to an eNB 101, a licensed assisted access (LAA) node (LAA-node), and a user equipment 103. The UE 103 would exchange data and control information with the eNB 101 through a licensed frequency band F1 which requires authorization by the eNB 101 for access. The eNB 101 may also transmit packets over the unlicensed frequency spectrum F2 to the UE 103.
The procedures for the eNB 101 to enable packets transmission over the unlicensed frequency band have been known as Licensed Assisted Access (LAA). In FIG. 1A, the eNB 101 may assigns the LAA Node 102 to exchanges data and/or control information with UE 103 in the unlicensed frequency spectrum F2. In some scenarios, the LAA Node 102 could be an independent entity which is physically separated from eNB 101 but utilizes a wired or wireless backhaul connection to communicate with the eNB 101. In other scenarios, the LAA Node 102 may also be a logical entity which is co-located with the eNB 101 (or physically situated within the eNB 101). Since the un-licensed frequency spectrum F2 would also be open to other UEs and other radio access technologies (RATs) for use, various regulations could be applied as for how the un-licensed bands F2 could be utilized in different countries or regions.
In some countries or regions, regulations may require the LAA Node 102 or the UE 103 to implement a “listen-before-talk” mechanism before delivering packets in the LAA-downlink (LAA-DL) or LAA-uplink (LAA-UL) direction. The LAA-DL path means that the LAA Node 102 would deliver packets to the UE 103 through one or more LAA channels over the unlicensed frequency band F2, and the LAA-UL path means that the UE 103 may deliver packets to LAA Node 102 through one or more LAA channels over the licensed frequency band F2.
Referring to FIG. 1A and FIG. 1B together, to transmit packets in the LAA-UL path, the UE 103 may periodically determine the channel condition of one LAA channel during a clear channel assessment (CCA) interval 111 which may occur periodically. In response to performing a CCA, the UE 103 would not transmit via unavailable channels 112 and would instead transmit via available channels 113. When the UE 103 detects a clean LAA channel during the CCA intervals 111a 111b, the UE 103 would start packet transmissions 114 in a clean LAA channel. A clean LAA channel could be defined as the average signal strength of interferences within a CCA interval being lower than a predefined threshold, which could be related to the hardware capability of the UE 103.
As shown in FIG. 1B, a UE in general may perform a CCA procedure in each of the CCA intervals 111 to ensure that there is no other radio signal transmission which may cause interference over a LAA channel. In each of the CCA intervals 111, a UE may perform a passive scan to detect energy level of any potential interference signal in the LAA channel. The validity of energy detection may depend on the sensitivity of the RF module on a LAA node or UE and may consequently influence the CCA range of a LAA Node/UE. A UE typically would not deliver packets when the UE has determined that a LAA channel has been occupied, which means that the average detected signal strength of an interference signal during a CCA interval has exceeded a predefined threshold. As shown in FIG. 1B, a UE would not transmit packets during idle periods 115 before a next CCA interval. In addition, the maximum time span of a packet transmission may also depend on regional regulations or regulations of different countries. In general, An LAA Node would also implement the same CCA and maximum time span for data transmission in the LAA-DL packet transmission as previously described.
FIG. 1C illustrates a part of an unlicensed band in U.S., India, Japan, Europe, and China. As shown in FIG. 1C, an un-licensed band would include a plurality of carrier frequencies and could be synonymous with LAA channels in this disclosure. Many countries may have regulations about the range of unlicensed bands in the frequency spectrum. Typically, an eNB may determine LAA channel selections for a LAA Node or UE to deliver user data in an unlicensed band. Before a LAA channel selection, a UE would measure and/or report the channel conditions of one or more LAA channels in the unlicensed band to the eNB, and thus the eNB would be able to procure the necessary information to select one or more LAA channels for a LAA-DL transmission.
There are many parameters that could be measured and/or reported by a UE or LAA node, such as the RSSI (Received Signal Strength indicator), RSRP (Reference Signal Received Power), RSRQ (Reference Signal Received Quality) level of the LAA channels, and etc. The RSSILAA parameter is measured by a UE and indicates the average total received power in the LAA channel. For, the RSRPLAA parameter, the RSRP is a RSSI type of measurement. An LAA Node would periodically broadcast reference signals, such as discovery reference signals (DRS) of LTE, in the occupied LAA channel. Subsequently, a UE would be able to measure the power of the LTE Reference Signals spread over the LAA channel. The measurement approaches of RSRPLAA could be similar to the measurement approaches of RSRP in the LTE licensed band. The RSRQLAA parameter indicates the received signal quality of the LAA channel. RSRQLAA may be proportional (or equivalent) to the ratio of RSRP and RSSI over the LAA channel.
For the LAA, a UE would need to measure and report LAA channel conditions to an eNB for LAA channel selection. FIG. 1D illustrates an example of RSSILAA measurement and report. Typically, a UE would perform a RSSILAA measurement in order to detect other (hidden) network terminals or nodes. In this example, the UE would perform measurements at subframes 1, 41, and 81. The measurement interval 121 is the duration between subframes 1 and 41. The report interval 122 is the duration between subframes 1 and 121 as the UE would report to the eNB at sub frame 121 for the average RSSI values measured in each symbol of the subframes 1, 41, and 81.
The LAA channel measurement and report could be triggered periodically because the source of interferences may appear in LAA channels in an unpredictable manner. Moreover, a UE may need to measure multiple LAA channels since there could be many candidate LAA channels for an eNB to select. It is noted that the LAA Node could also measure LAA channel conditions and report such to an eNB. For a LAA-DL packet transmission, a LAA Node may also provide a LAA_Node measurement report to an eNB for LAA channel selection. Subsequently, an eNB may also obtain LAA channel conditions from both the “LAA_Node measurement report” and “LAA_UE measurement report”. The contents of a “LAA_Node measurement report” could be the same as that of a “LAA_UE measurement report”. Moreover, the same information such as information of a neighbor interfering node (as indicated by the RSSILAA of a LAA channel) may also be covered by the LAA_Node measurement and LAA_UE measurement report when one interfering node interferences both the LAA Node and UE. Therefore, it might not be necessary for a UE to report all the LAA channel conditions when it is relatively close to the LAA Node. Based on the above described observation, the mechanism of measurement reporting and reporting rules could be enhanced in order for a UE to decrease the overhead of LAA channel measurements and reports.